Ende, H.T.M. van den

Lagraauw, R.

Mannetje, D.J.C.M. 't

Mugele, F.

Otten, S.

Pit, A.M.

't Mannetje, Dieter

Pit, Arjen

van den Ende, Henricus T.M.

Mugele, Friedrich Gunther

NARCIS 

Droplet trapping and control on a single EWOD surface

University of Twente Research Information

Droplet trapping and control on a single EWOD surface Dieter ‘t Mannetje, Rudy Lagraauw, Simon Otten, Arjen Pit,  Dirk van den Ende and Frieder Mugele d.j.c.m.tmannetje@tnw.utwente.nl  Introduction & setup Electrowetting droplet trap - Two electrodes separated by a small gap provide an electrically tunable pinning center for droplets sliding down an inclined plane.  - At low voltages the droplets can pass the trap, above a certain critical voltage UC (that increases with the inclination angle α) the droplets get trapped. In this work, we investigate the critical conditions for trapping of drops.   U α g - Droplet trapping can be achieved and is repeatable as function of viscosity, size,…          ->  Droplets can be filtered based on viscosity/size/… - Trapping is modelled to predict the trapping threshold   - By changing the trapping geometry and using multiple electrodes, droplets can be steered/sorted Rescaled trapping diagram. The lines give the predicted transition depending on how the pinning is reduced by electrowetting.  Inset: zoom on glycerol:water droplets  Droplet trapping can be modelled as a damped harmonic oscillator (l=diameter of drop, a=electrode gap): Surface: tape+silicon oil (θa=95o, θr=92o) α=3-15o Water droplets moving over the trap: U<<UC (blue), U<UC (red), U>UC (purple) and U>>UC (black).  Potential energy in green => Overshoot means inertia is important Trapping phase diagram for water droplets of 20/40/60 µl (diamonds/circles/squares) A similar graph can be made for droplets of a 8:1 glycerol:water mixture 𝑚𝑥 + 𝜆𝑥 + 𝑘𝑥 = 𝑚𝑔 sin 𝛼 − 𝐹𝑝   0 100 200 300 4000123456  V [cm/s]U [V]Go Stop water U<Uc: Go U>Uc: Stop Time  U -1012-4 -3 -2 -1 0 1 2 3 4-20246 V [cm/s]x [mm] Potential Energy (a.u.)Conclusion 0 1 2 3 4 5 6 7 8012345  V/VrefU/Urefg glycerol water  Additional effect: Contact angle hysteresis is reduced by AC electrowetting so in the trap Drop sorter with 4 final positions using 5 electrodes Modelling g Drop sorter Next to the control parameters inclination angle, voltage, and drop size the inertia of the drop is found to also play an important role for millimeter-sized water drops   U up 𝐹𝑝 𝑈 = 𝐹𝑝 0 − 𝑐𝑈2 𝑘 = potential depth =𝜀𝜀𝑟𝐴𝑑 ∗ 𝑙(𝑙 − 𝑎)𝑈2 𝐹𝑝 = pinning force = 𝜎 ∗ 𝑤 ∗ (𝑐𝑜𝑠𝜃𝑅 − 𝑐𝑜𝑠𝜃𝐴) 𝐹𝑝 02 𝐹𝑝 0  𝜆 = friction coefficient 𝑈𝑟𝑒𝑓 =𝜆2𝑑(𝑙 − 𝑎)𝜀𝜀𝑟𝑚𝑙 𝑉𝑟𝑒𝑓 =𝜆(𝑙 − 𝑎)4𝑚 

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Droplet trapping and control on a single EWOD surface

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University of Twente Research Information